Power amplifiers including one or more of various types of field effect transistors may be used for converting dc-input power into radio frequency (RF) power. At high voltages, the amplifiers may have a tendency for out-of-band high-frequency oscillation due to a negative resistance band at the output of the amplifier. Under RF drives, this high-frequency oscillation may manifest itself as spurious signals at in-band frequencies near the carrier frequencies. For high-power microwave systems (e.g., radar and wireless communications applications), it generally is desirable for the frequency spectrum to be free of these spurious signals at all frequencies.